The long-term objective of this research project is to develop a technique of somatic gene therapy in which endothelial cells that have undergone gene transfer ex vivo are transplanted into the capillary bed of skeletal muscle. This technique of somatic gene therapy could be used to achieve a regional or systemic effect by co-or repopulating a vascular bed with endothelial cells which constitutively or inducibly express a protective recombinant protein such as tissue plasminogen activator or Factor IX. Thus, the development of such a technique of somatic gene therapy could have a wide application to both surgical and genetic human deceases. The Specific Aims of the project are: Aim I: To identify and characterize the molecular mechanism mediating the adhesion of endothelial cells seeded onto quiescent, confluent endothelial cell monolayers. Aim II; To optimize the adhesion and incorporation of genetically transduced endothelial cells transplanted into the capillary bed of skeletal muscle. Aim III; To document long-term recombinant gene expression by endothelial cells transplanted into the capillary bed of skeletal muscle. The investigators have considerable experience with an in vitro model to study endothelial cell-endothelial cell adhesion as well as with an in vivo rt model to study transplantation of genetically modified endothelial cells into skeletal muscle capillary beds. The proposed experiments to achieve th above Aims include identification and characterization of specific adhesion molecules mediating endothelial cell-endothelial cell adhesion. These experiments would reveal fundamental new knowledge concerning endothelial cell-endothelial cell interactions. This knowledge could also be used to enhance adhesion and incorporation of transduced endothelium into the capillary wall. In a rat model the adhesion and incorporation of genetically transduced endothelium transplanted into the capillary bed will be optimized by angiogenesis induced with injection of basic fibroblast growth factor or stimulation f skeletal muscle regeneration. Finally, the optimal techniques of transplantation of transduced endothelium into host capillary beds, determined in the aforenoted studies, will be used to document the efficacy of this technique to deliver recombinant proteins into the circulation. At the completion of these studies, this technique of somatic gene therapy will be ready for evaluation in a primate model in preparations for its use in humans.